Added new setting `rememberPlaytime`

This adds a new setting called `rememberPlaytime`. It enables developers to disable the hash and localStorage usage to store the current play time. The standard value for this is `true`, so the behavior does not change from the current.

I've added this to the defaults in `podlove-web-player.js`, to `readme.md`, `readme.txt` and `standalone.html`. Please let me know if something is missing.